Interdecadal Change of Relationship between North Atlantic Oscillation and Tropical Cyclone Genesis Frequency over the Western North Pacific

Abstract This article investigates the relationship between spring (March–May) North Atlantic Oscillation (NAO) and the tropical cyclone genesis frequency (TCGF) over the western North Pacific (WNP) from June to November. It is found that their relationship appears insignificant from 1950 to 1971, intensifies significantly from 1972 to 2010, and then weakens again since 2011. The interdecadal change of this relationship is strongly influenced by the meridional displacement of the North Atlantic jet stream (NAJS). During 1972–2010, the NAJS is located southward, facilitating the spread of Rossby wave energy to the equatorial region and enhancing the NAO impact on sea surface temperatures (SSTs) over the tropical North Atlantic (TNA). Generally, positive (negative) phases of the NAO relate to negative (positive) TNA SST anomalies in spring, subsequently triggering positive (negative) SST anomalies in the central Pacific through the wind–evaporation–SST feedback. The central Pacific SST anomalies, intensifying from summer to autumn, lead to a basin-uniform circulation anomaly over the WNP and ultimately control the WNP TCGF. Conversely, in the other two periods, owing to the northward shift of the NAJS, the influence of the NAO is constrained to the extratropics, thereby disrupting the linkage between the NAO and TNA SST anomalies. As a result, the interannual relationship of spring NAO with the WNP TCGF weakens. The decadal meridional shift of the NAJS is supposed to be associated with the phase transition of the Pacific decadal oscillation. Significance Statement To enhance the understanding of the relationship between tropical cyclones and mid- to high-latitude climate systems, we explore how the North Atlantic Oscillation affects the genesis frequency of tropical cyclones in the western North Pacific and why their relationship encounters interdecadal changes. We propose that the North Atlantic Oscillation can trigger sea surface temperature anomalies over the tropical North Atlantic during spring, which subsequently affect the tropical cyclone formation over the western North Pacific in summer and autumn. Importantly, this relationship experiences interdecadal changes, aligning with changes in the meridional shift of the North Atlantic jet stream which may be related to the phase change of the Pacific decadal oscillation. Understanding these dynamics is crucial for climate predictions and addressing the potential impacts of extratropical systems on tropical cyclones.